New Study Shows MRI can Perform Forensic Age Estimation on Human Teeth
Refugees are people who have fled war, violence, or persecution in their home nations and crossed international borders to find safety in another country. The age of a refugee dictates the procedure the country an individual has entered will follow. However, these people often leave their homes with very few possessions, rarely arriving with proof of age, such as their birth certificate. Therefore, forensic age estimation (FAE) is frequently performed for courts and government authorities to act in accordance with the law.
FAE involves measuring certain aspects of a person’s teeth and comparing these findings to reference values. Tooth development is mostly complete by 13 years of age. Third molar (wisdom teeth) eruption occurs between 17–21 years of age but does not occur in every person. Therefore, FAE is generally focused on degenerative tooth characteristics.
Secondary Dentine Formation
Teeth are made up of three hard tissues, enamel, cementum, and dentin, and one soft tissue, dental pulp. Odontoblasts are found between the soft dental pulp and hard dentin and produce dentin. There are three types of dentin: primary, secondary, and tertiary. Primary dentin forms before tooth eruption, secondary dentin forms after tooth eruption, as the tooth develops with age, and tertiary dentin is produced in response to trauma.
Secondary dentine is added to the dentine facing the dental pulp, gradually reducing the volume of the dental pulp cavity during a person’s life. In addition, unlike tertiary dentine, it is thought to be independent of external factors, such as trauma. Therefore, measuring the volume of dental pulp is a common method in FAE.
Measuring Dental Pulp Reduction Using MRI
The measurement of dental pulp volume by cone-beam computed tomography (CBCT) has been heavily reported. This technique produces a three-dimensional (3D) dataset that can reconstruct the tooth structure. However, CBCT requires high radiation exposure. In recent years, the use of magnetic resonance imaging (MRI) has shown promise for FAE as it is a radiation-free method, but challenges remain as hard structures, such as teeth, are difficult to analyze due to their low water content, resulting in ultrashort T2 relaxation times.
Ultrashort time echo (UTE) MRI is a relatively recent technique that may be able to overcome this issue as it can characterize substances with very short relaxation times, down to 40 µs. It has been shown to analyze hard tissues, such as cortical bone, at relatively high spatial resolution and high signal-to-noise ratio. A group of researchers at University Hospital Münster, Germany, used an ultrahigh field 9.4 T Bruker Biospec 94/20 MRI to analyze extracted human teeth and determine whether UTE-MRI is suitable for FAE.
UTE-MRI Produces High-Quality Data of Hard and Soft Tooth Tissue
One of the most important parameters in dental imaging is image quality, as fine details often need to be identified. This study was able to achieve an in-plane spatial resolution of 66 μm3, which is comparable to the resolution of CBCT. This high spatial resolution enabled the soft dental pulp up to the apical foramen to be distinguished from the other tooth tissue and the sample embedding material, resulting in detailed images for all four types of human teeth: front, canine, premolar, and molar.
Using semi-automatic segmentation and the different intensities of the structures of the MRI data set, 3D reconstruction of the data was possible and allowed for the dental pulp volume to be calculated for all four types of human teeth. This analysis was also able to show that dental pulp, especially the root pulp can have varying formations; root canals can separate and converge within the root canal.
UTE-MRI Can Be Used For FAE
These data show promise for UTE-MRI to be able to achieve 3D imaging of teeth, with high spatial resolution, and dental pulp volume quantification in a variety of different teeth. However, the sample size of this study was small, with only four human teeth being analyzed. Therefore, this research is planning to be repeated with a much larger sample size, which will enable the method to be tested for its ability to determine the age of a tooth when compared to a reference library.
Other potential limitations of this technique are that field strengths in a clinical setting can currently only reach 7 T, and UTE-MRI is not yet widely available. However, with its significant advantage over CBCT as a radiation-free analysis and the highly promising preliminary data presented in this study, UTE-MRI has the potential to become the routine method of choice for FAE in the future.
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References
- Timme, M., et al. (2020). Evaluation of Secondary Dentin Formation for Forensic Age Assessment by Means of Semi-automatic Segmented Ultrahigh Field 9.4 T UTE MRI Datasets. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-020-02425-7.
